The present invention generally concerns the television art and the processing of synchronizing signals within the television receiver. More particularly, the present invention concerns the separation of such signals from the transmitted composite video signal under varying signal conditions, including a varying DC sync level in the composite video signal.
Various systems have been utilized previously for separation of sync signals from composite video signals. At least one such system is described in detail in U.S. Pat. No. 4,621,289, issued Nov. 4, 1986 for an invention entitled Digital Sync Separator And Differentiator. In that system, the sync signals are separated from the composite video signal by comparing the video signal to a DC reference voltage which is generated depending upon the particular characteristics of the received video signal. As such, that system provides a recognizable advance in the art with particular application to digital sync applications in which composite sync may be separated from the composite video despite noisy, weak, or nonstandard signal conditions. However, as recognized by the description of the system in that patent, that system is responsive to the DC level detection. Accordingly, signal recognition difficulties may arise in the presence of swings in the input DC level of the composite video signal, particularly rapid and dramatic DC swings in the sync tip levels. This can result in a nonrecognition of the sync signal or, equally bad, a false recognition of video signals as synchronizing signals.
Accordingly, it is a principal object of the present invention to provide an improved sync separator system which generally overcomes the deficiencies present in the prior art.
It is a further object of the present invention to provide an improved sync separator system which may provide the advantages of sync separation based upon input signal characteristics while reducing the overall sensitivity to variations within the input signal.
It is still a further object of the present invention to provide an AC coupled sync separator system having filtered DC feedback means for providing stabilized sync separation based upon input signal characteristics without an undue sensitivity to input DC level changes.